1. Field of the Invention
The present invention relates to a process system for treating a contaminated liquid, more particularly groundwater, to remove toxic volatile organic compounds (VOCs), objectionable volatile inorganic compounds (VICs) and surfactants from said liquid. The process system of this invention removes VOCs, VICs and surfactants in one apparatus and represents a low cost and highly effecient alternative to present groundwater treatment technology which is expensive and causes secondary air pollution.
About 70 percent of potable water in the U.S.A. is supplied by groundwater. Groundwater contamination, which is a national major concern, is about 71 percent caused by industrial accidents (chemical spills, tank leaks, etc.), 16 percent caused by railroad or truck's chemical accidents, and 13 percent caused by leachates from lagoons or dumpsites.
The primary reasons for treating groundwater are: potable use (39 percent), clean-up of aquifer to prevent spread of contamination (48 percent), and industrial and commercial use (13 percent). In any case, the potentially hazardous VOCs must be removed. Timely clean-up of aquifer to prevent spread of contamination is extremely important because the damage can be beyond repair if the spread of contamination is too wide.
Toxic organic compounds commonly found in groundwater include, but are not limited to, the following:
______________________________________ Organic Compounds Percent of Concentration in Groundwater Occurrences Range ______________________________________ Carbon tetrachloride 5 130 ug/l-10 mg/l Chloroform 7 20 ug/l-3.4 mg/l Dibromochloropropane 1 2-5 mg/l DDE 1 1 ug/l DDT 1 4 ug/l CIS-1,2-dichloroethylene 11 5 ug/l-4 mg/l Dichloropentadiene 1 450 ug/l Diisopropyl ether 3 20-34 ug/l Tertiary methyl-butylether 1 33 ug/l Diisopropyl methyl phosphon- 1 1,250 ug/l ate 1,3-dichloropropene 1 10 ug/l Dichloroethyl ether 1 1.1 mg/l Dichloroisopropylether 1 0.8 mg/l Benzene 3 0.4-11 mg/l Acetone 1 10-100 ug/l Ethyl acrylate 1 200 mg/l Trichlorotrifloroethane 1 6 mg/l Methylene chloride 3 1-21 mg/l Phenol 3 63 mg/l Orthochlorophenol 1 100 mg/l Tetrachloroethylene 13 5 ug/l-70 mg/l Trichloroethylene 20 5 ug/l-16 mg/l 1,1, 1-trichloroethane 8 60 ug/l-25 mg/l Vinylidiene chloride 3 5 ug/l-4 mg/l Toluene 1 5-7 mg/l Xylenes 4 0.2-10 mg/l EDB 1 10 ug/l Others 1 NA ______________________________________
Other common contaminants in groundwater include: volatile inorganic compounds (VICs), surfactants, iron, manganese, calcium hardness, magnesium hardness, coliform bacteria, and virus.
The present technologies for groundwater treatment include: air stripping tower without air emission control, non-regenerative gas phase granular activated carbon, chemical oxidation, non-regenerative liquid phase granular activated carbon, active charcoal fiber, biological processes, ion exchange, ultrafiltration, H.sub.2 O.sub.2 treatment, reverse osmosis (RO), ozonation, lime softening, ultraviolet (UV), chemical coagulation, sedimentation, filtration and chlorination. Air stripping tower without air emission control is the most common process for VOCs removal, but is not acceptable in many states. Liquid-phase granular activated carbon (GAC) contactor is technically feasible for water purification, but may be economically unfeasible when it is used alone. Chemical oxidation alone or UV alone is not cost-effective for VOCs reduction. Certain chemicals may even give undesirable residuals. Ultrafiltration and RO are excellent post-treatment process, requiring adequate pretreatment for cost reduction. Biological process is very efficient for removal of organic contaminants, but causes air pollution and requires thorough disinfection.
While conventional ozonation, UV, RO and chlorination are all effective disinfection processes, they all require separate reactors.
The present invention represents a package apparatus for removal of VOCs, VICs and surfactants, and is also an efficient and cost-effective groundwater purification system which considers the affordability, performance, governmental acceptance, secondary pollution elimination and simplicity in operation.
2. Description of the Prior Art
The most common process system for removal of volatile organic compounds (VOCs) from groundwater includes flow equalization, pH adjustment, chemical coagulation, flocculation, sedimentation, filtration, conventional air stripping tower, liquid phase granular activated carbon (GAC) adsorption, and gas phase granular activated carbon adsorption. Conventional air stripping tower can also be replaced by ozonation, ultraviolet (UV), and hydrogen peroxide for VOCs reduction.
Flow equalization requires a separate equalization tank. Chemical coagulation and pH adjustment are done in a rapid mixing tank.
Flocculation is accomplished in a slow mixing tank. Sedimentation clarifier generally requires long detention time, and a large land space. Filtration is the tertiary pretreatment prior to conventional air stripping tower. pH adjustment is an important pretreatment step for ammonia removal. Chemical coagulation, flocculation, sedimentation and filtration together are required for reduction of iron, manganese and hardness prior to conventional air stripping and conventional liquid phase GAC for VOC removal.
Conventional air stripping tower is a simple desorption process used to lower the VOCs of a liquid stream. In the process, the contaminated liquid is pumped to the top of a tall packed tower with a countercurrent flow of air drawn through the bottom openings. VOCs are stripped from the falling water droplets into the air stream which is then discharged to the atmosphere. The effluent of air stripping tower is thus purified to lower VOCs and ammonia. For removal of ammonia which is a VIC, lime or caustic soda must be added in a pretreatment tank prior to the conventional air stripping to raise the pH of the liquid to the range of 10.8 to 11.5 converting essentially all ammonium ions to ammonia gas which can then be stripped by air. For removal of VOCs and ammonium ions, a pretreatment process system comprising of chemical coagulation/flocculation, sedimentation and filtration, is generally required prior to the conventional air stripping tower to remove iron, manganese and hardness which, otherwise, will clog the conventional air stripping tower, in turn, will reduce air stripping efficient. Conventional air stripping towers do not recycle their gaseous effluent; therefore, they require air emission control facilities. In addition to high capital cost, conventional air stripping towers have other problems and limitations: (a) poor efficiency in cold weather locations having air temperature below 10 degree C.; (b) not working in freezing conditions unless sufficient heated air is available; (c) objectionable air emission due to ammonia and VOCs discharge into air environment; (d) poor removal efficiency when VOCs and ammonia concentrations in the liquid are low; (e) scale formation due to high iron, manganese and hardness contents in the liquid; (f) objectional tall construction, (g) process restriction for simultaneous combined treatment using chemicals and ultraviolet lights (UV), and (h) incapable of removing surfactants.
The gaseous effluent from a conventional air stripping tower is generally treated by gas phase granular activated carbon (GAC) contactors which can not be regenerated in-situ for reuse.
The liquid effluent from a conventional air stripping tower is commonly further treated by a liquid phase GAC contactor which can not be regenerated in-situ for reuse, and therefore its operating cost is high.
The process system and apparatus of this invention significantly simplifies the process system for removal of volatile organic and inorganic compounds from groundwater or other liquids. The flow equalization, pH adjustment, chemical coagulation, enclosed dispersed gas stripping, supplemental chemical oxidation, UV, recycled gas emission control, wet scrubbing, and GAC regeneration are all accomplished in one package unit for cost saving. The post-treatment for final polishing of the liquid stream by a liquid phase GAC contactor can be added, but is no longer absolutely required. Besides, both the liquid phase GAC for liquid treatment and the gas phase GAC for gas emission control are regenerative in situ for reuse and further cost saving. Recycling of purified gas, for reuse in the enclosed dispersed air stripping reactor eliminates the air pollution problem.
Conventional air stripping tower can not be cost-effectively operated in conjunction with ozonation, UV and hydrogen peroxide because separate reactors are required. The enclosed dispersed gas stripping chamber of the present invention, however, incorporates pH adjustment, gas stripping, ozonation, UV and hydrogen peroxide treatment into one reactor for more efficient removal of both VOCs and VICs.
In order to clarify the dissimilarities between the present invention and the prior arts, many direct and cross references are reviewed and cited.
Prior process for substantially eliminating dissolved oxygen from a liquid and from a shipping container is described in U.S. Pat. No. 3,946,534, issued Mar. 30, 1976 to Richard S. Egly, which relates to repeated operation by purging the container with inert gas, pressurizing with the gas and then releasing the pressure and repeating the steps for a plurality of times. Egly's patent is particularly directed to elimination of oxygen gas from a liquid, rather than to elimination of toxic volatile organics and volatile inorganics (such as ammonia) from a liquid. However, it is important to illustrate the development of the gas stripping art leading to the present disclosure.
Prior process for recovering volatile organics from exhaust gases or spent air containing these compounds using a layer of silica containing adsorbents is shown in U.S. Pat. No. 4,323,372 issued Apr. 6, 1982, to Rolf Bentz et al. The present invention relates to a process and apparatus for removing VOCs, VICs and surfactants from a liquid and also for automatic gas emission control using a foam collector, a wet scrubber and a gas phase GAC contactor which has self-regeneration capability and recycles its purified effluent for the purpose of gas stripping in an enclosed chamber.
A prior process for treating liquid with powdered adsorbent, and one or more biological packed towers is described in U.S. Pat. No. 4,407,717 issued Oct. 4, 1983 to Gerald H. Teletzke et al. The present invention discloses an improved liquid treatment process and apparatus using an enclosed dispersed gas stripping chamber, a foam collector, a wet scrubber and GAC contactors, but no biological packed towers.
The method and process for combined physicochemical and biological treatment of wastewater using powdered activated carbon (PAC) in an open sequencing batch reactor (SBR) is disclosed by Wei-Chi Ying et al in U.S. Pat. No. 4,623,464 issued Nov. 18, 1986, and in U.S. Pat. No. 4,755,296, issued Jul. 5, 1988. Their method and process removes VOCs from wastewater by PAC adsorption and biological reaction, and converts ammonia (VIC) to nitrate ions. The present invention relates to an enclosed reactor for gas stripping, disinfection and gas emission control, and for direct removal of ammonia and surfactant. Besides the present invention is feasible for drinking water treatment, wastewater treatment or groundwater decontamination.
An air purification process is disclosed by Thomas E. Vara et al in U.S. Pat. No. 4,689,054, issued Aug. 25, 1987. The Vara process includes the steps of particulate filtration, adsorption, desorption, separation, incineration and venting. The present invention does not include the steps of particulate filtration, separation, incineration and venting, and relates to groundwater decontamination, potable water treatment and industrial effluent treatment which all with built-in air emission control.
A system for treatment of and mass transfer in liquid/gas mixtures, especially removal of oxygen from seawater, is disclosed by Norolf Henriksen in U.S. Pat. No. 4,752,306, issued Jun. 21, 1988. Henriksen's patent involves oxygen removal by an inert stripping gas. The present invention relates to utilization of air or oxygen for oxidation of ferrous iron and manganese, and for stripping mainly VOCs and VICs from groundwater, in which oxygen is added, not reduced.
A method for separating volatilizable contaminants from soil is disclosed by Adam L. Sigerson et al in U.S. Pat. No. 4,715,965, issued Dec. 29, 1987, which does not relate to the enclosed dispersed air stripping for both liquid treatment and gas emission control as in the case of the present invention.
A two-stage process for purifying wastewater containing organic and adsorbable pollutants in open tanks is disclosed by William M. Copa et al in U.S. Pat. No. 4,810,386, issued Mar. 7, 1989. Their disclosed process includes the steps of aerating the wastewater in the presence of powdered activated carbon (PAC) and biologically active solids in aeration zone, and subsequently settling the suspended solids by gravity in quiescent zone. Their oxygen is provided only for biological growth in opened tanks. The present invention relates to mainly physical separation of VOCs, VICs and surfactants by innovative gas bubble stripping (with any kind of gas) in an enclosed reactor, and physical adsorption of VOCs by regenerative GAC, and chemical adsorption of VICs.
Chang et al disclose a process for removal of volatile organic compounds from vapor streams using a binderless carbon molecular sieve adsorbent in U.S. Pat. No. 4,820,318, issued Apr. 11, 1989. Another method and apparatus for separating and recovering volatile solvents from vapor streams also using molecular sieve adsorbent is disclosed by Stefan Schweitzer et al in U.S. Pat. No. 4,846,852, issued Jul. 11, 1983. The present invention relates to a process for removal of both VOCs and VICs from both liquid and gas streams by gas stripping UV, scrubbing and regenerative GAC.
Still another method and equipment for recovering volatile organic compounds (VOCs) from exhaust waste gas using active charcoal in fiber form is disclosed by Georges Fritsch in U.S. Pat. No. 4,859,216, issued Aug. 22, 1989. Fritsch's patent further relates to adsorption-desorption steps for active charcoal fiber regeneration and a recirculation step for the gaseous regenerating fluid through the system. The present invention relates to an enclosed dispersed gas stripping process for mainly liquid treatment with built-in gas emission control, and utilizes combined pH adjustment, chemical reaction, UV, stripping, absorptive scrubbing, and regenerative GAC adsorption (instead of active charcoal fiber adsorption) to remove VOCs, VICs and surfactants from a liquid (instead of removing only VOCs from an exhaust waste gas). Furthermore, in the case of the present invention, the purified gas stream (instead of the gaseous regenerating fluid) is recirculated to the enclosed dispersed gas stripping chamber for liquid treatment.
Meidl discloses a process system for water decontamination by conventional air stripping tower, biological open reactor containing PAC, sedimentation/thickening and wet air oxidation, in U.S. Pat. No. 4,857,198, issued Aug. 15, 1989. The present invention relates to a liquid treatment process system comprising the steps of enclosed dispersed air stripping, GAC adsorption, scrubbing, chemical reaction, and UV, which are aimed at VOCs and VICs removals.
A similar method and system for decontaminating groundwater or other water, is disclosed by Paul C. Miller in U.S. Pat. No. 4,892,664, issued Jan. 9, 1990. Miller's patent relates a process comprising of conventional air stripping tower for groundwater treatment and catalytic oxidation for air purification. Conventional air stripping tower requires pretreatment for pH adjustment, and removal of iron, manganese, and hardness, and requires post-treatment for disinfection. Besides, conventional air stripping tower removes only VOCs and can not receive the gaseous effluent from catalytic oxidation for repeated air stripping. The present invention relates to mainly the enclosed dispersed gas stripping reactor for removal of VOCs, VICs and surfactants from a liquid. The enclosed dispersed gas stripping as in the case of the present invention has built-in pretreatment, post-treatment and recirculating air emission control capabilities.
The method for the deoxidation of chlorinated water, more particularly sea water, by means of a low oxygen content stripping gas and a liquid absorbent is disclosed by Charles Mandrin et al in U.S. Pat. No. 4,937,004, issued Jun. 26, 1990. The present invention relates to a process for removal of both VOCs and VICs (instead of chlorine only) from a liquid (instead of specifically chlorinated sea water) by means of a high oxygen content stripping gas (instead of a low oxygen content stripping gas).
A single-stage continuous aeration-batch sedimentation clarification process in open tanks for purifying wastewater is disclosed by Curtis D. Cooley in U.S. Pat. No. 4,952,316, issued Aug. 28, 1990. Cooley's patent further relates to the use of PAC in the aeration step. The present invention relates to the enclosed dispersed air stripping process (instead of aeration-sedimentation clarification in open tanks) for both liquid treatment as well as air emission control (instead of only for liquid treatment), and also relates to GAC contactors (instead of only PAC). Furthermore, Cooley's process is only for purifying wastewater. The process disclosed by the present inventors is feasible for drinking water treatment, groundwater decontamination, and industrial effluent treatment.
A continuous chemical pretreatment, aeration and ultrafiltration process for purifying dairy wastewater is disclosed by Massoud Pirbazari et al in U.S. Pat. No. 4,956,093, issued Sep. 11, 1990. Their patent also relates to the use of PAC in the aeration step. The present invention is mainly for treatment of either potable water or non-potable water (instead of only dairy wastewater) by an enclosed dispersed air stripping reactor (instead of an open aeration tank containing biological solids and PAC) and GAC contactors (instead of PAC alone). Furthermore, the process disclosed by the present inventors does not require the use of a chemical pretreatment tank and an ultrafiltration post-treatment unit.
Schumacher et al disclose an apparatus and process for adsorbing VOCs from the flue gas of a combustion unit in one reactor and regenerating adsorbent material in another reactor both for air emission control. Their process system specifically includes adsorption, combustion, humidification, condensation, and heating. The present invention relates to stripping both VOCs and VICs from liquid by an enclosed dispersed air stripping reactor, adsorbing/absorbing VOCs from the gaseous reactor effluent, adsorbing the remaining VOCs from the liquid reactor effluent, regenerating GAC, and recycling the purified gas stream for further stripping.